The industrial and laboratory-scale production of carbon nanotubes (CNTs) has been increasing for the last decade, with current production volumes at 1,300 tons year−1 globally (ton=106 g) (e.g., with a doubling rate of once every two years and assuming that the CNT mass: US $ ratio is unchanged over the next ten years). Many known methods for large-volume CNT production, including catalytic chemical vapor deposition (CVD), are plagued by inefficiency where no more than about 3% of the introduced carbon feedstock is converted to CNT. In some cases, the unused feedstock is recycled for subsequent nanotube growth, but in many other cases, the effluent and its associated by-products are vented to the atmosphere. These untreated materials could amount to an annual release of 41,000 tons (41×109 g) of carbonaceous material, and this may expand to 1,300,000 tons year−1 (1.3×1012 g year−1) within the next decade if production accelerates as predicted.
Additionally, for many methods, heating the feedstock gas at high temperatures is necessary for rapid CNT growth in order to generate critical CNT precursor molecules. Recent studies have demonstrated that the effluent from an ethene-based CVD growth, i.e., by thermal treatment of common CNT feedstock gasses (C2H4/H2), contained several compounds that pose threats to the quality of the air, water and soil. These include toxics (e.g., benzene, 1,3-butadiene, and aromatic hydrocarbons), greenhouse gases (e.g., methane), and compounds that contribute to smog formation and exacerbate respiratory illness.